Deliberately grounded on a tiny reef in the South China Sea, part of an island chain claimed by the two Asian countries, the Sierra Madre is now the unlikely base for a detachment of Filipino marines who stand guard over the atoll, scanning the turquoise waters for Chinese ships.

Just reaching this unusual landmark, located 105 nautical miles (194 kilometers) from Palawan province in the western Philippines, is a nerve-jangling experience.

We approached the submerged reef in our aging wooden fishing boat at top speed — 11 knots per hour. From the north, a modern Chinese coast guard ship was closing in at least twice as fast with the intention of blocking our path. A second Chinese vessel quickly approached from the south with the same idea.

But they didn't make it. After several tension-filled minutes, we entered the shoal, which was too shallow for the larger Chinese boats to follow. Some of the fishermen on our boat prayed in relief – it doesn't always happen this way.

It's probably fair to say not many people have heard of the Second Thomas Shoal, which is known as Ayungin in the Philippines and Ren'ai Jiao in China. This teardrop-shaped reef is part of the Spratly Islands, a mostly uninhabited archipelago midway between the Philippines and Vietnam, claimed entirely by China and in its various parts by the Philippines, Brunei, Malaysia, Taiwan and Vietnam.

To complicate matters, the conflict has sucked in the United States, which has a mutual defense agreement with the Philippines and is urging a peaceful resolution. It has also prompted closer security ties between the Philippines and Japan, which is itself at loggerheads with China over islands in the East China Sea.

While some of these disputes focus on little more than clusters of uninhabited rock, the outcome of this territorial wrangling has the potential to sway the balance of power across the region. The value of some of these territories actually lies under the seabed with pockets of natural gas and oil — as we've seen recently with the deployment of oil exploration rigs by China off the Paracel Islands — another disputed chain in the South China Sea.

Getting to the Second Thomas Shoal took months of negotiations with Philippine authorities – because of logistical and security concerns – and then seven days traveling by boat.

I started the odyssey in April this year in Puerto Princesa, the capital of Palawan province. I was traveling with Eugenio Bito-Onon Jr., the mayor of Kalayaan, the smallest and one of the poorest municipalities in the Philippines. It consists of 10 tiny islets and reefs situated at the northern tip of the Spratlys.

We were headed for Pag-asa first, the only island in the area with a civilian population. It was also the staging point for reaching the Sierra Madre. Usually based in Puerto Princesa, Bito-Onon only manages to travel to Pag-asa once a year. We stopped at a few smaller islands on our journey, each home to small detachments of marines from the Philippines — the last line of defense against foreign encroachment.

Some of those marines admitted it was a lonely mission but said they were proud to serve in such a remote outpost in defense of Philippines territory. Others claimed it was "fun and exciting" to monitor foreign ships, mostly Chinese, moving into their waters.

At the end of the third day of our journey, we finally arrived in Pag-asa, the second-largest island in the Spratlys. Previously a military base, the Philippines government encouraged civilians to move here in 2002. More than 12 years on, and 120 people now live alongside the small units of Philippines air force, navy and marines still stationed here.

Jacqueline Morales, 28, moved to the island from Palawan with her husband and two children. She wanted to serve her country and heard that Pag-asa was in desperate need of teachers. While residents' living costs are partially subsidized by the central government, she admitted the "China factor" is a real worry.

"I watch television. We know the Chinese are interested in the island," she said. "We are prepared here just in case China attacks us. The school was assigned as an evacuation center. I am nervous because it might happen. What will happen to us?"

(CNN)